Polls are regular content entries in a section. To create your first poll, go to 'Entries' and select 'polls'. Click the 'New entry' button.
Then, you can enter the question for the poll, and enter the possible answers.
Since the poll is a regular content entry, all the usual features will work: you can set an expiry date and enable the poll on a per-site basis.
Now your poll is ready to be published.